I think the key to noticing the differences also requires the understanding that the differences will be subtle…noticeable to those that have good critical listening skills. I myself was a skeptic until I encountered some hum on a previous tube amp that I owned. I ended up buying a relatively cheap Furman Power Conditioner and the hum definitely decreased significantly. It didn’t fix the hum entirely, but it eliminated enough of it for me to consider it a worthwhile purchase.
When it comes to cables, once again the differences are subtle. As a one time huge skeptic, I used to think such things were snake oil. But then I started thinking about my Bass Guitar and amp. A good cable has improved the noise floor and blackness and tone of my bass guitar in the past, so why wouldn’t that be true for audio and headphones?
The thing that makes this a polarizing subject is that it involves subjectivity. But in addition to that, some people may not have the proper tier headphones and gear to hear the difference. Case in point, when I purchased some audioquest rca cables, I didn’t notice a difference with my Asgard 3/Modius stack…but I could tell a difference with my Soekris dac1321/Violectric HPA V200 stack.
Again I will reiterate that the differences are subtle and nuanced and can be easily missed if one isn’t paying attention or doesn’t have the best critical listening skills.
One last thing I will say is that these subtle differences and whether or not the cost of cables /power conditioner/etc. is worth it or not, can only be decided based on what you yourself are hearing and whether or not you have the money to spend on these items without causing yourself hardship. Those are all things that are uniquely personal, and whether or not one is a skeptic or a believer has no bearing on each individuals own experiences and monetary situation.
Last thing I will say to the hardest skeptics is that even if it is placebo, if one is willing to shell out the money for these placebos, that shouldn’t impact you or affect you. So let’s all agree that as long as one enjoys their gear and headphones, that is all that should matter. After all, nobody has to live with my headphones and gear other than me.